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Patterns of Heredity. Incomplete Dominance, Codominance and Sex-linked. Figure 14.2 Mendel tracked heritable characters for three generations. Genetics Vocabulary. - PowerPoint PPT Presentation
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Patterns of Heredity
Incomplete Dominance, Codominance and Sex-linked
Figure 14.2 Mendel tracked heritable characters for three generations
Genetics Vocabulary• Incomplete Dominance - a form of
intermediate inheritance in which one allele for a specific trait is not completely dominant over the other. If the trait is incomplete it will be stated in the problem.
(Some people, like incomplete dominance, use superscripts or subscripts w/ diff letters)
Figure 14.9 Incomplete dominance in snapdragon color
Genetics Vocabulary• Codominance - A condition in which
both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other. If the trait is codominant it will be stated in the problem. (When crossing codominant traits, use different capital letters) RR RW WW
Autosomes vs. Sex-chromosomes
Sex-linked traits• Most human traits are inherited by passing
autosomes – non-sex chromosomes– (just like peas)
• Sex-linked traits = inherited by passing sex-chromosomes.– Many human diseases including:
• Hemophilia & Color blindness
Designating Sex-Linked Traits
XA = normalXa = the trait (a genetic disease or abnormality)Y = Y chromosome (males only)
* X-linked traits are only on the X chromosome
Genotype Phenotype
XA XA Normal female
XA Xa Normal female, also called a carrier
Xa Xa Female with trait
XA Y Normal male
Xa Y Male with trait
• X-linked traits may also skip generations
• Males are affected more often than females because they only have one X chromosome
Sample problem
• Hemophilia is an X-linked disorder. If an affected father and a carrier mother have a boy, what is the probability that boy will have hemophilia?
What is the probability that boy will have hemophilia?
Mother’s Genes
Xa XXa
Y
XaXa XaX
XaY XY
Fa
the
r’s
Gen
es
Autosomal Dominant diseases
• Individuals have the trait if they have the dominant allele.– Ex: familial
hypercholesterolemia– Huntington’s disease– Dwarfism– Neurofibromatosis– Colon cancer– Kidney disease– Etc.